Microwave sintering carbon nanotube/Ni0.5Zn0.5Fe2O4 composites and their electromagnetic performance

Carbon nanotube (CNT)–Ni0.5Zn0.5Fe2O4 powders were prepared by in situ chemical precipitation and hydrothermal processing, and further sintered by microwave sintering technology. The results show that CNTs acted as ‘heating source’ and promoted the consolidation of composites during the microwave sintering process. However, too much CNTs (such as 5 wt%) led to phase decomposition and reduction of ferrite materials because of the ultra-high localized temperature building up in the interface of CNTs and ferrite grains. The electrical conductivity of composites increased by more than seven orders of magnitude when compared to that of pure Ni0.5Zn0.5Fe2O4, and remained a high value at the temperature of 70 K (for example, 1 wt% CNT/Ni0.5Zn0.5Fe2O4 sample kept conductivity of 0.1 S/m). The saturation magnetization was strongly dependent on the mass percentage of CNTs. With the increase in CNT content, both the real and the imaginary permittivity were increased in the frequency region 0.6–5 GHz (L and S bands). According to the measured results of ϵ r and μ r , the frequency-dependent reflectance loss (RL) of CNT/Ni0.5Zn0.5Fe2O4 composite ceramics with different CNT content was evaluated. The CNT-doped ferrite ceramics discussed herein is very promising to be used in an on-beam-line high-order mode (HOM) load in particle accelerators based on superconducting RF due to their excellent low-temperature characteristics.